Ctla-4 transcriptional activation: regulation of induced expression

<p>Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is a T cell surface protein that is homologous to CD28 and binds to the B7 family of ligands. Unlike CD28, CTLA-4 interaction transmits a negative signal in T cells, leading to suppression of proliferation. CTLA-4 is constitutively expressed on regulatory T cells (Tregs) but is also inducible in effector T cells. The mechanisms driving transcriptional regulation of CTLA-4 are poorly understood. Our previous work identified a bona fide NFAT1 binding site in the proximal promoter for effector T cells. In addition, we found histone acetylation occurred after stimulation.</p> <p>As a result of its role in suppressing T cell proliferation, CTLA-4 is important for regulation of T cell responses. CTLA-4-immunoglobulin fusion proteins have shown efficacy to quell the overactive immune system in various types of autoimmune diseases. Alternatively, blocking antibodies to CTLA-4 have been used in cancer therapies to boost the anti-tumor immune response. Malignant cells of cutaneous T cell lymphoma (CTCL) express elevated levels of CTLA-4, which may contribute to reduced</p> <p>tumor immunity as the disease progresses. The objective of this work was to identify mechanisms of transcriptional regulation of CTLA-4 to better understand how this gene can be modulated to potentially cater the immune response for a variety of immune-mediated diseases.</p> <p>The major findings of this work include a mechanism by which proteasome inhibition augments CTLA-4 transcription in normal primary human CD4 T cells. The Th2 associated transcription factor GATA3 is both elevated and activated by phosphorylation after treatment with the proteasome inhibitor bortezomib, which in turn leads to CTLA-4 transcriptional activation in primary CD4 T cells. This finding may in part explain the increase in CTLA-4 found in CTCL, where GATA3 is also more abundant, particularly in its phosphorylated state. The increased CTLA-4 in our primary cell model is capable of suppressing T cell proliferation, demonstrating the potency of transcriptional modulation of this gene. Additionally we explored epigenetic and topological modifications that occur for CTLA-4 activation. We found the histone acetyltransferases p300 is responsible for histone 3 acetylation at the CTLA-4 promoter, and its activity is required for CTLA-4 transcription. We also discovered a previously undiscovered role for topoisomerase I in expression of a variety of induced genes, including CTLA-4. These results define novel mechanisms governing transcriptional activation of CTLA-4 in human effector CD4 T cells.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Open Access Dissertation

Discipline thesis:degree_discipline

Immunology and Microbiology

Year dc:date.available

2011

Author dc:creator

• Gibson, Heather

Contributors dc:contributor

• Henry K. Wong
• Wei-Zen Wei

• Immunology and Infectious Disease

Repository record dc:identifier

https://digitalcommons.wayne.edu/oa_dissertations/237

OAI identifier oai:identifier

oai:digitalcommons.wayne.edu:oa_dissertations-1236